agreement of noun and adjective

Question

Why is it  "après-midis entières" and not "entiers" since "midi" is masculine?

Accepted Answer

Bonjour Kathleen,
Maarten's answer is correct! Both are accepted whilst L'Académie française does prefer the masculine form. In the exercise, both are accepted too. 
Attention: 'whole + plural noun'

des après-midis entières/entiers = whole afternoons
des après-midis tout entières/entiers = whole afternoons

I hope this is helpful.
Bonne journée !

Answer

"après-midi' is one of those unusual nouns (compound in this case), that can be either masculine or feminine, even though midi itself is masculine and the Académie-Française 'prefers' masculine - did you check whether both were accepted ? They should be.

(The plural form 'après-midis' has been accepted since the 'rectifications' in 1990)

Answer

Just to clarify the situation with apres-midi - some dictionaries still list it only in 'singular' form and as 'invariable', however the plural form as 'apres-midis', adding the extra 's' and equivalent to 'afternoons' in English, is now also quite correct.